A process is disclosed in U.S. Pat. No. 4,708,990 wherein a living polymer of the alkenyl type is end-capped with an arylcyclobutene monomer end-capping agent. Secondary polymerization of the polymer can then be induced by heating.
U.S. Pat. No. 5,034,485 discloses a polymeric composition produced by the reaction of, for example, styrene in a free radical polymerization reaction which is initiated by a cyclobutarene peroxide, wherein the cyclobutarene fragments are incorporated into the polystyrene polymer. A further polymeric product can be produced from the polymeric composition of the free radical polymerization by ring opening polymerization of the cyclobutarene moiety to produce branched, crosslinked or a mixture of branched and crosslinked polymers. The use of this technique requires the synthesis and use of the cyclobutarene peroxide.
U.S. Pat. No. 4,724,260 discloses polymeric compositions comprising in polymerized form, a monomer containing a polymerizable arylcyclobutene moiety, and a polymerizable unsaturated alkyl moiety; wherein the monomer is polymerized by subjecting it to conditions sufficient to polymerize the unsaturated alkyl moiety. A related disclosure in U.S. Ser. No. 872,334 exemplifies copolymers of vinylbenzocyclobutene and styrene.
U.S. Pat. No. 4,698,394 discloses a solid random copolymer comprising from about 99.99 to about 80 mole percent of a monoalkenyl arene monomer and from about 0.01 to about 20 mole percent, based on total moles of incorporated monoalkenyl arene monomer and olefinic benzocyclobutene monomers, an olefinic benzocyclobutene of the formula: ##STR1## where R.sub.1 is hydrogen or CH.sub.3 and R.sub.2 is (CH.sub.2).sub.n where n is 0 to 6. Copolymers of vinylbenzocyclobutene and styrene are exemplified.
EP Publication 0425814 discloses syndiotactic homopolymers of an arylcyclobutene functional monomer and syndiotactic copolymers of an arylcyclobutene functional monomer and a vinylaromatic monomer are prepared by polymerizing the monomers in the presence of a catalytic amount of a suitable coordination catalyst such as the reaction product of polymethylaluminoxane and a transition metal compound. Copolymers of styrene and 3-vinylbenzocyclobutene exemplified are insoluble in o-dichlorobenzene after the side rings of the arylcyclobutene are opened and crosslinked.
High molecular weight polystyrene has improved creep resistance, elasticity, higher heat distortion, lower permanent set, higher flexural, and impact strengths. This improves its utility for molding objects which require impact resistance and the ability to bend without breaking. High molecular weight polystyrene is generally accepted to be polystyrene with a molecular weight of above 300,000.
One may increase the molecular weight of a polystyrene by the methods disclosed in U.S. Pat. Nos. 4,698,394 and 4,724,260. When the copolymers of vinylbenzocyclobutene and styrene taught therein are heated the side rings of the benzocyclobutenes open and react with each other. This increases the polystyrene molecular weight. However the levels of benzocyclobutene taught convert the polymers to thermosets. That is they crosslink at such a density that their melt viscosity at normal process temperature levels is too high to be useful. They also become insoluble in solvents and may even gel in the polymerization reactor.
The gel point or gel state is described in the Concise Encyclopedia Of Polymer Science And Engineering; Wiley Interscience, 1990, pp. 430-2, which is incorporated herein by reference. The gel point describes a critical point in the polymerization from a monomer to a fully cured polymer. The liquid polymer before the gel point is called a sol because it is soluble in good solvents. The solid polymer beyond the gel point is called a gel. It is not completely soluble, even in a good solvent. However low molecular weight fractions (sol fraction) may still be extractable.
Preferably the gel point is defined as that point wherein one part of polymer will not completely dissolve after contact with one hundred parts of methylene chloride at 25.degree. C. for fifteen minutes.
One may increase the molecular weight of a polystyrene made in a given reaction by lowering the polymerization temperature. The polymer has more desirable properties but the amount of polystyrene made in a given reactor is reduced because of longer polymerization times required at lower temperatures.
It would be desirable to increase the molecular weight of a alkenyl arene polymer such as polystyrene without forming a thermoset or gels and without reducing the capacity of the polystyrene polymerization reactor.
While arylcyclobutene and cyclobutarene are both used to represent the same moiety the term cyclobutarene is more correct since the `cyclobutene` side ring is saturated. Both terms are commonly used by the artisan and understood to have the same meaning.